The conventional optical interferometric surface profilometer has been developed mainly for static measurement of nano-scale three-dimensional surface profiles. It has been widely employed for measuring surface roughness and uniformity on semiconductor wafers, depth of laser marks, metal-bump size and co-planarity during flip chip bonding, size and height of spacers in liquid-crystal display panels, and surface profile of fiber end-face and micro optical devices. Moreover, there are some low-coherent optical interferometric techniques capable of using a vertical scanning method enabled by a piezoelectric ceramics displacement sensor to measure broken heights that are not possible by conventional phase shifting method. In recent years, vibratory measurement has been incorporated into the optical interferometric surface profilometer, thus widening its applications in observing and measuring the vibratory behavior of functional elements and thin-films in micro-electro-mechanical system (MEMS) and micro-opto-electro-mechanical system (MOEMS) industries.
Although optical interferometer had been used in a vast range of applications for making precise measurement on parts being manufactured or used in those applications, the measurement resulting from such optical interferometer can be severely affected by environment vibration as it is inevitable during the operation or manufacturing of those parts, such as display panels, wafers, MEMS parts or optical parts. Under normal circumstance of measurement, even the slightest vibration can cause severe effect on the interferometric result even when the measurement is protected by anti-vibration facilities. Not to mention that the object being measured itself can sometimes being affected by certain voluntary vibration or be induced to vibrate passively which are not controllable by any anti-vibration facility. Therefore, there are already many researches in every advanced countries efforting to eliminate or reduce the adverse affect on the interferometric measurement caused by vibration.
One of which is an interferometric measurement apparatus having reduced sensitivity to vibration disclosed in U.S. Pat. No. 5,589,938, that it is capable of using two interferograms obtained from two cameras respectively by a fast and a slow data acquisition rates for reducing its sensitivity of measurement to vibration. Another such research is an interferometric method disclosed in U.S. Pat. No. 6,624,894, in which a reference signal is used to track the actual behavior of the scanner in an interferometer to produce scanner-position data that can be used to correct errors introduced by scanner nonlinearities and other error sources. Moreover, in U.S. Pat. No. 7,321,430, a vibration resistant interferometric method is provided that it is capable of using an internal sensor or external sensor to determine the scanning position of its piezoelectric ceramics displacement sensor in an interferometer.